In her strongest comments so far about Erdogan's statement, Merkel said the Nazi comparisons were "sad" and "so incredibly misplaced that one really can't comment, but they cannot be justified."

German Chancellor Angela Merkel (L) and Turkish President Recep Tayyip Erdogan during their meeting in Istanbul. Germany said on November 25, 2016

"We will not allow the victims of the Nazis to be trivialized," she said. "These comparisons with the Nazis must stop."

Erdogan made the comment on the weekend after several German municipalities canceled rallies that Turkish Cabinet ministers had planned to address in support of a national referendum to give the Turkish president more powers. Officials have cited problems with overcrowding and fire safety, and other issues.

Mrs Merkel said the provocative comparisons to the Nazis were deeply unhelpful

About 1.4 million people of Turkish descent living in Germany are eligible to vote in the referendum.

In a step back from the heated rhetoric of recent days, Turkish Prime Minister Binali Yildirim told reporters in Ankara Thursday that Germany seems to be taking sides in the upcoming referendum, but he did not repeat the Nazi comparison.

Asked about Merkel's comments, Yildirim said Germany "may be disturbed" that a yes vote is likely in the referendum, but that if it is interfering in the process it amounts to "meddling" in another country's affairs and is "very wrong."

He told the AP that the way ahead "doesn't lie in any more public statements that are made from one side or the other."

"Rather Germany should take steps to get rid of the restrictions we are currently facing in terms of the access we have to millions of voters living in those countries," he said.

Turkish Foreign Minister Mevlut Cavusoglu, who himself had repeated Erdogan's Nazi comments, backtracked somewhat in Ankara on Thursday, saying nobody was calling Merkel or other German leaders Nazis.